Add sufficient water to completely cover the cereal (it's not an exact measurement - you can add as much as you like as iron doesn't dissolve in water)

Mash the cereal with a spoon or mix it with the water using a blender. The more finely ground the cereal is, the easier it will be to get the iron.

Stir the magnet through the crushed cereal. Iron is heavy and will sink, so be sure to pay attention to the bottom of the bowl. If you used a blender, make sure you can get to the particles at the bottom of the jar.

Look for the black 'fuzz' or iron on the magnet. It's easiest to see the iron if you wipe the iron on a white napkin or paper towel. Mmmm Mmm Good :-)